1. Field of the Invention
The invention relates to apparatus and methods for reducing non-uniformities of a shaft, such as the drive shaft of an internal combustion engine.
2. Description of the Related Art
In particular in internal combustion engines, nonuniformities occur in the rotation of the engine-driveshaft, which are due primarily to the gas and mass forces of the engine. Such rotational nonuniformities can impair the riding comfort, e.g., in a vehicle, and lead to wear on the drive system as well as other parts of the vehicle.
Therefore, it has already been proposed to outfit an internal combustion engine with a system for active reduction of rotational nonuniformities. The action of such a system is based on the fact that an electric machine or an electric brake generates an alternating torque, or even one which only pulsates in one direction, which is directed opposite the rotational nonuniformities and thereby reduces them. Examples of such systems are disclosed by Patent Abstracts of Japan, Volume 11, No. 28 (M-557), Jan. 27, 1987 and JP-A-61 200 333 (NISSAN I), Patent Abstract of Japan, Volume 4, No. 29 (M-002), Mar. 14, 1980 and JP-A-55 005 454 (TOYOTA), EP-B-0 427 568 (ISUZU), DE-A-32 30 607 (VW), EP-B-0 175 952 (MAZDA), Patent Abstracts of Japan, Volume 7, No. 240 (M-251), Oct. 25, 1983 and JP-A-58 126 434 (NISSAN II), DE-A-41 00 937 (FICHTEL and SACHS) and EP-A-0 604 979 (NIPPONDENSO).
In the above-mentioned EP-B-0 175 952 (MAZDA), the electric machine is a commutator machine with two separate rotor windings, one of which serves to operate the machine as a motor and the other to operate it as a generator. Since the machine is alternately operated as a motor and as a generator in brief time windows, it alternately generates positive and negative torques, which are directed opposite the rotational nonuniformities and which cancel each other out on average. In the intervals of time between two windows the machine is passive and generates no torque. The publication also mentions the possibility that the electric machine can support the internal combustion engine while accelerating and braking the vehicle. This is done through changes in the relative duration of the motor and generator time windows, i.e., through changes in the timing relations of motor and generator operation for constant magnitude of the particular motor and/or generator torque. For example, if the electric machine is supposed to support the engine while accelerating, the time windows for the generator operation are shortened and those for the motor operation are lengthened. The electric machine then generatesxe2x80x94averaged out over a periodxe2x80x94a positive torque. To generate a negative torque on average, the time windows for the motor operation are correspondingly shortened and those for the generator operation are lengthened. Also in EP-A-0 604 979 (NIPPONDENSO), the superpositioning of a vibration dampening function and a generator function can be accomplished by a timing relation (so-called duty cycle) other than one for the motor and generator operation, without changing the magnitude of the particular motor and/or generator torque.
The following, more remote state of the art does not pertain to the active vibration dampening: DE-A 33 35 923 (VW II), EP-A 0 437 266 (MAGNET-MOTOR), DE-A 32 43 513 (VW III), DE-A 33 38 548 (VW IV), DE-A 44 08 719 (VW V), W. Geissler, F. Unger-Weber: xe2x80x9cModeling the Three-Phase Propulsion System of a Modern Multisystem Locomotive,xe2x80x9d EPE, Florence, 1991, p. 4-632 to 4-637, and J. Langheim, J. Fetz: xe2x80x9cElectric Citybus with Two Induction Motorsxe2x80x94Power Electronics and Motor Control,xe2x80x9d ETEP, Vol. 2, No. 6, November/December 1992, p. 359 to 365.
With the systems of the two above-mentioned publications it is possible in theory to have the electric machine also generate a nonvanishing (on average) positive or negative torque, while reducing rotational nonuniformities.
A system for active reduction of rotational nonuniformities of a shaft, especially the drive shaft (10) of an internal combustion engine (1) or a shaft that is coupled or can be coupled to it, comprising at least one electric machine (4), especially a rotary-field or traveling wave machine, which is coupled or can be coupled to the shaft, wherein the electric machine (4) is controlled such that
it generates a rapidly varying torque, to reduce the rotational nonuniformities, and
it superimposes on this torque a positive or negative torque in order to further achieve a driving action or braking or generator type action.